Polymeric stabilizers for polyvinyl chloride resin

ABSTRACT

A polyvinyl chloride composition having superior processing and thermal stability properties is prepared by blending with the polyvinyl chloride a copolymer of an α-olefin and an unsaturated epoxy monomer, or a terpolymer of an α-olefin, an unsaturated epoxy monomer and an epoxy-free monomer, such as an acrylate ester.

This is a division of application Ser. No. 585,485, filed June 10, 1975.

BACKGROUND OF THE INVENTION

Polyvinyl chloride (PVC) is presently used in myriad usefulapplications; some such applications involve the introduction of hotsubstances into containers molded from a PVC composition. ConventionalPVC compositions contain additives such as liquid epoxy type stabilizers(e.g. epoxidized soybean oil). These stabilizers, when blended into thePVC resin, have a tendency to reduce the glass transition temperature(Tg) of the PVC compound; thus decreasing the softening temperature ofthe processed PVC product. This decrease in softening temperature leadsto problems where hot substances are introduced into PVC products suchas bottles; the bottles tend to sag and distort.

The instant invention overcomes these problems by blending with PVC, anepoxy type stabilizer system that results in a PVC composition with a Tgequal to or greater than the Tg for the PVC composition without theepoxy type stabilizer. More specifically, the instant invention teachesblending with PVC either a copolymer of an α-olefin and at least oneunsaturated epoxy monomer or optionally blending with PVC a terpolymercomprised of the aforementioned copolymer plus an epoxy-free monomerwherein the epoxy-free monomer can also be an α-olefin.

Copolymers of unsaturated epoxy monomers and ethylene have been longknown in the art. For example, U.S. Pat. No. 3,383,372 (Spivey)discloses a copolymer comprised of ethylene and glycidyl esters such asglycidyl acrylate, glycidyl methacrylate and glycidyl ethacrylate. Thesecopolymers, as taught by Spivey, are either used alone or are modifiedwith fillers and plasticizers as molding compositions for themanufacture of films and coating.

Another reference to copolymers of unsaturated epoxy monomers is foundin U.S. Pat. No. 3,201,497 (Heino). This reference relates to epoxyresin adhesive compositions comprised of an epoxy resin, a copolymer ofan ethylenically unsaturated epoxy monomer and an ethylenicallyunsaturated epoxy-free monomer and a curing agent for the epoxy resin.

SUMMARY OF THE INVENTION

It has surprisingly been found that when copolymers of an α-olefin andan unsaturated epoxy monomer or a terpolymer of an α-olefin, anunsaturated epoxy monomer and an epoxy-free monomer (which can also beanother α-olefin) are blended with PVC, a composition is produced havingsuperior processing and thermal stability properties. This new PVCcomposition also has a softening temperature higher than that forconventional PVC compositions containing liquid epoxy type stabilizers,thus enabling the production of a PVC container which will have lesstendency to sag or distort when filled with hot substances. For example,the maximum use temperature for a PVC bottle produced from aconventional liquid stabilizer such as epoxidized soybean oil is about55° C to about 65° C whereas the maximum use temperature for a PVCbottle produced with stabilizer systems of the instant invention wouldbe about 65° C to about 75° C.

DETAILED DESCRIPTION

The term "PVC" as used in this invention is meant to include bothhomopolymers of polyvinyl chloride and co- and ter-polymers of vinylchloride with comonomers such as vinyl acetate, vinyl formate, alkylvinyl ethers, ethylene, propylene, butylenes, vinylidene chloride, alkylacrylates and methacrylates, alkyl maleates, alkyl fumarates, etc.Preferably, at least 80%, and more preferably 100% of the monomers to bepolymerized will be vinyl chloride monomer. These resins have a numberaverage molecular weight of about 35,000 to about 120,000; preferablyfrom about 45,000 to about 75,000. Inherent viscosity (as measured byASTM D1243-60; Method A) will generally be in the range of about 0.5 toabout 1.5, preferably in the range of about 0.7 to about 1.2. The methodof preparation of these resins is not critical and, for example, any ofthe well known suspension techniques may be employed.

Unsaturated epoxy type monomers suitable for use in the instantinvention are those which will free radically polymerize with α-olefins.These include but are not limited to glycidyl methacrylate, allylglycidyl ether, glycidyl acrylate, vinyl glycidyl phthalate and allylglycidyl phthalate. The preferred unsaturated epoxy monomers areglycidyl acrylate, and glycidyl methacrylate.

The epoxy-free monomers suitable for optional use in the presentinvention include, but are not limited to acrylate and methacrylateesters of C₁ to C₁₈, preferably C₁ to C₁₂ alcohols such as methylmethacrylate, ethyl acrylate, butyl methacrylate; styrene andsubstituted styrenes; acrylonitrile; vinyl esters of C₁ to C₁₈,preferably C₁ -C₁₂ aliphatic monocarboxylic acids such as vinyl acetate,vinyl propionate and vinyl stearate; and α-olefins. Preferred are thealkyl acrylates and methacrylates and most preferred are the lowmolecular weight acrylates and methacrylates such as methyl and ethylacrylate and methyl and ethyl methacrylate.

α-olefins suitable for use in the instant invention are generally the C₂to C₂₀ α-olefins. Preferred are ethylene and propylene.

A typical formulation for the instant composition is as follows: about 1to about 50 parts, preferably 2 to 20 parts of a copolymer of anα-olefin and an unsaturated epoxy monomer; or about 1 to about 50 parts,preferably 2 to 20 parts of a terpolymer of an α-olefin, an unsaturatedepoxy monomer and an epoxy-free monomer, based on 100 parts of PVC. Itis also understood that other ingredients such as pigments, dyes,fillers, flame retardants, impact modifiers, lubricants, processingaids, stabilizers and other conventional compounding ingredients can beincorporated into the vinyl chloride resin compositions in anyconvenient manner, for example by the use of high speed mixers orinternal mixers.

It is to be understood that the copolymers and terpolymers of instantinvention can be either prepared by copolymerization or by grafting theepoxy and/or epoxy-free monomer onto a polyolefin. It is also within thescope of this invention that the α-olefin and epoxy-type monomer can befirst copolymerized and subsequently grafting the epoxy-free monomeronto the resulting copolymer or vice versa the epoxy-free monomer can becopolymerized with the α-olefin to which the epoxy-type monomer isgrafted onto the resulting copolymer.

The compositions of the present invention are produced by firstpreparing the epoxy/α-olefin copolymer or terpolymer by procedures knownin the art. For example, these copolymers can be prepared bypolymerizing mixtures of α-olefin and unsaturated epoxy monomer eitherin tubular or autoclave reactors at pressures above about 30atmospheres, for example, about 500 psi to about 2500 psi; preferably ata pressure of about 1100 psi and at temperatures from about 37° C toabout 210° C. Where the copolymer is a graft copolymer, thepolypropylene or polyethylene may first be fed into a plastics extruderwherein it is pressed and heated to a flowable or molten condition attemperatures between 130° and 250° C, and above the crystalline meltingpoint of the polymer, under pressure. The epoxy monomer and initiator isthen fed under pressure into a midsection of the barrel of the extruderand into contact with the heat-plastified or molten polymer.

Initiators suitable for use in the instant invention include: organicperoxides such as caprylyl peroxide, lauroyl peroxide, benzoyl peroxideand ditertiary butyl peroxide; organic hydroperoxides such as t-butylhydroperoxide and cumene hydroperoxide; azocompounds such asazo-bis-isobutyro-nitrile; pivalates such as t-butyl peroxy pivalate;and peroxy dicarbonates such as diisopropyl-peroxydicarbonate. Preferredare the organic peroxide and hydroperoxides. The amount of initiatorsuitable for use in the instant invention is about 0.01 to about 2.0percent based on the total weight of monomer.

It is preferred that the above-aforementioned epoxy-α-olefin copolymeror terpolymer be prepared so as to give a product in powder form. Anyconventional process known in the art for giving the powder form of saidpolymer can be used. Such a polymer in powder form allows a moreconvenient procedure when blending with the PVC resin compound which isalso preferred to be in powder form. It will be evident to those skilledin the art that the practice of this invention is not limited to theepoxy copolymer or terpolymer or even the PVC resin being in powderform. The materials of the present invention may also be in pellet orany other conventional form and it will also be evident to those skilledin the art that the type of blending apparatus is determined by the formof the material before blending.

Before the epoxy polymer is incorporated into the PVC compound, the PVCcompound is first prepared by conventional means known in the art. Ifthe ingredients are in the preferred powder form, they are dry blendedon a high speed mixer such as a Papenmeier; or Henschel mixer at mixerspeeds ranging from about 500 rpm to about 5000 rpm. It is preferredthat the mixer speed be about 500 to about 1000 rpm during the firstminute of mixing and thereafter the speed increased to about 1000 toabout 2000 rpm for the remainder of mixing time; overall mixing timeusually ranges from about 5 to about 30 minutes. The order of mixing is,however, not critical and variations may be made if desired, but atypical order of mixing is shown in Table I below.

                  TABLE I                                                         ______________________________________                                                               Temperature Time                                       Order  Additive        (° C)                                                                              (Min.)                                     ______________________________________                                        1      Resin           32-38       1                                          2      Stabilizer,     60          5                                                 (processing aid)                                                       3      Impact Modifier 82          5                                          4      Copolymer or     90-110     5                                                 terpolymer                                                             5      Transfer from hot                                                                             70-95       5                                                 mixer to cool mixer                                                    ______________________________________                                    

If the epoxy polymer is in powder form, it may be dry blended with theabove PVC resin and various ingredients in a high speed mixer. If theepoxy polymer is in pellet form or any other bulk form, then it isevident to those skilled in the art that such materials can be blendedin a Banbury, an extruder, a rubber blender or even in a Brabender asused in the examples of the instant application.

The term glass transition temperature (Tg) as used in the instantspecification and claims means the temperature at which the amorphousdomains of a polymer take on the characteristic properties of the glassystate; that is, brittleness, stiffness and rigidity. In other words, itis the temperature at which the polymer changes from a plastic state toa brittle, vitreous state or vice versa.

All glass transition temperature measurements of the instant inventionwere made on a Perkin Elmer Differential Scan Calorimeter (DSC model1B). All samples were vacuum dried for 36 hours at 0.1 mm Hg beforeanalyzing.

BRABENDER STABILITY TEST

The Brabender Heat Stability Test used to determine the long rangeprocessing stability of the instant PVC compounds was performed on aBrabender torque rheometer fitted with a 30 ml roller head (5/2) and a 5kg ram weight. A Moseley Autograf Model 7101B recorder was used tocontinuously monitor the temperature.

The Brabender conditions were as follows:

Head Temperature:177° C

Sensitivity:5:1

Zero Suppression:to keep pen on scale

Damping at X 1:15 secs. (1000-100 mg)

Rotor Speed:35 and 143 rpm

Scale:X 5

Sample Charge Weight:22 g

The Brabender was set at 35 rpm and 22 gr of PVC compound was chargedthrough a cooled chute wherein the ram weight was applied. When the ramweight reached bottom, the Brabender and Moseley chart weresimultaneously started. One minute after fusion, the rotor speed wasincreased from its original speed of 35 rpm to 143 rpm as quickly aspossible. When the torque rose 100 meter grams, the test wasdiscontinued.

BRABENDER FUSION TEST

Another test used on the compositions of the instant invention is theBrabender Fusion Test. This test was performed on a Brabender aspreviously described in the Brabender Stability Test. The Brabenderconditions for the Fusion Test were as follows:

Head Temperature:215° C

Sensitivity:5:1

Zero Suppression:to keep pen on scale

Damping at X 1:20 sec. (1000-100 mg)

Rotor Speed:25 rpm

Sample Charge Weight:23 g

The Brabender was set at 35 rpm and 23 gram of PVC composition wascharged through a cooled chute wherein the ram weight was applied. Whenthe ram weight reached bottom, the Brabender and Moseley chart weresimultaneously started. Two minutes after fusion torque peak, the testwas discontinued.

The invention will be further understood by reference to the followingdescription and examples.

EXAMPLES 1 - 5

A dry blend according to the Basic Formula in Table II was prepared in ahigh speed Papenmeier mixer by first mixing at a speed of 1200 rpm for 1minute then further mixing for an additional 2 minutes at a speed of3600 rpm.

                  TABLE II                                                        ______________________________________                                        BASIC PVC FORMULA                                                             Ingredient           phr                                                      ______________________________________                                        PVC resin.sup.(a)    100                                                      Impact Modifier.sup.(b)                                                                            15                                                       Processing Aid.sup.(c)                                                                             3                                                        Stabilizer I.sup.(d) 2                                                        Stabilizer II.sup.(d)                                                                              1                                                        Lubricant I.sup.(e)  1.25                                                     Lubricant II.sup.(f) 0.25                                                     Lubricant III.sup.(g)                                                                              0.5                                                      Lubricant IV.sup.(g) 0.5                                                      ______________________________________                                         .sup.(a) Resin of PVC homopolymer with a number average molecular weight      of about 50,000.                                                              .sup.(b) Mainly polymethyl methacrylate - an impact modifier.                 .sup.(c) Methyl methacrylate - butadiene - styrene terpolymer (MBS) - a       processing aid.                                                               .sup.(d) Organotin - thermal stabilizers.                                     .sup.(e) Glyceryl monostearate - lubricant.                                   .sup.(f) Low molecular weight polyethylene - lubricant.                       .sup.(g) General lubricants such as stearates or stearic acid.           

To the basic formulation above, four separate samples were preparedaccording to Table III.

                  TABLE III                                                       ______________________________________                                        Additions to Basic Formulation                                                Sample                                                                        ______________________________________                                        E-1   Basic formulation only                                                  E-2   Basic formulation plus 5 phr Epoflex 945 (an                                  epoxidized soybean oil).                                                E-3   Basic formulation plus 5 phr of a copolymer                                   of polypropylene and glycidyl acrylate (2 wt %).                        E-4   Basic formulation plus 5 phr of a graft copolymer of                          low density polyethylene and glycidyl acrylate                                (1 wt %).                                                               Sample                                                                        E-5   Basic formulation plus 5 phr of a terpolymer of                               polypropylene, polyethylene (6 wt %) and glycidyl                             acrylate (2 wt %). Made by grafting glycidyl                                  acrylate onto a polypropylene polyethylene                                    copolymer.                                                                    All weight percentages based on the total weight                              of the co- or terpolymer.                                                     Brabender stability and fusion tests were run ac-                             cording to the method previously set-forth, and the                           results are found in Table IV and V.                                    ______________________________________                                    

                  TABLE IV                                                        ______________________________________                                        Brabender Stability Test                                                      Time to          Breakdown                                                    Sample                                                                              Breakdown, min.                                                                              Torque,mgm  Temp., ° C                            ______________________________________                                        E-1   14.5           1530        216                                          E-2   17.0           1300        217                                          E-3   20.1           1250        212                                          E-4   13.5           1430        218                                          E-5   18.2           1210        209                                          ______________________________________                                    

This table shows that the use of copolymers of this invention with PVCcomposition generally results in an increase in stability. Also evidentin this table is that for stability purposes, the epoxidized soy beanoil when used as a stabilizer in PVC compositions is substantiallyequivalent to the co- and terpolymers of the instant invention.

                  TABLE V                                                         ______________________________________                                        Brabender Fusion Test                                                                    Fusion Torque Peak                                                 Sample       Torque mg     Temp. ° C                                   ______________________________________                                        E-1          2200          320                                                E-2          2200          310                                                E-3          1120          295                                                E-4          1690          314                                                E-5          1400          301                                                ______________________________________                                    

This table shows the advantages of using the copolymers of the instantinvention as indicated by the lower torque values needed to reach fusionpeak as opposed to the composition containing the epoxidized soybean oilor the base composition without the use of any additional stabilizer.The lower torque values can be interpreted to mean that suchcompositions would require less work to flux and therefore easierprocessability.

Glass transition measurements were performed on samples E-1 to E-5 byuse of a differential scanning calorimeter (DSC). The results are foundin TABLE VI below.

                  TABLE VI                                                        ______________________________________                                        Glass Transition Determinations                                                                Glass Transition                                             Sample           (Tg, ° C)                                             ______________________________________                                        E-1              72.0                                                         E-2              63.5                                                         E-3              74.0                                                         E-4              77.0                                                         E-5              74.5                                                         ______________________________________                                    

This table illustrates the most critical aspect of the instantinvention, which is, the fact that the glass transition temperature of aPVC composition is not lowered when the stabilizers of the instantinvention are used. In fact, the glass transition temperature issurprisingly increased. This increase in glass transition temperature isimportant because it also correlates to an increase in softeningtemperatures, which also correlates to a PVC container which will lesslikely sag or distort when filled with hot substances.

EXAMPLES 6 - 8

24 grams of glycidyl methacrylate were placed in an autoclave 1 gallonreactor along with 1050 ml of cyclohexane into which 1100 psi ofethylene was introduced over a period of 1.5 hours at a temperature ofabout 105° C. 10 grams of lauroyl peroxide were introduced into saidreactor over a period of 1.5 hours. The copolymer was recovered and itsphysical properties measured; the results are shown in Table VII.

                  TABLE VII                                                       ______________________________________                                        PROPERTIES OF COPOLYMER OF EXAMPLE 6                                          Product Weight            156 g                                               Melting Point             102° C                                       Saponification No. (ASTM D-94)                                                                          25.8                                                Glycidyl Methacrylate (GMA)wt%                                                                          6.5                                                 Epoxide Equivalent, moles/kg                                                                            0.65                                                Calculated wt % GMA In Resin                                                                            9.0                                                 ______________________________________                                    

The Epoxide Equivalent was determined by dissolving 1.7 g of the aboveprepared copolymers in methyl ethyl ketone and refluxing for 10 minutesand subsequently titrating with 1 normal HCl. The following formula wasused to calculate the Epoxide Equivalent: ##EQU1##

Two separate blends were prepared by dry blending 5 phr of Epoflex 945(E-7) and 5 phr of the previously prepared ethylene/glycidylmethacrylate copolymer (E-8) with the Basic Formulation of Table II in ahigh speed Papenmeier mixer by first mixing at a speed of 1200 rpm for 1minute then further mixing at a speed of 3600 rpm for an additional 2minutes. E-6 represents only the Basic Formulation of Table II.

Brabender stability and fusion tests were run as previously describedand the results are shown in Table VIII and IX.

                  TABLE VIII                                                      ______________________________________                                        Brabender Stability Test                                                                                          Torque                                           Fusion               Time to Before                                           Peak       Torque    Breakdown                                                                             Breakdown                                 Sample Time,sec   mgm       min     mgm                                       ______________________________________                                        E-6    40         3150      10.5    1600                                      E-7    45         2850      17.2    1500                                      E-8    240        1200      17.6    1450                                      ______________________________________                                    

                  TABLE IX                                                        ______________________________________                                        Brabender Fusion Test                                                                Fusion Peak                                                            Sample   Time,sec    Torque,mgm  Temp, ° C                             ______________________________________                                        E-7      12          2050        165                                          E-8      18           450        169                                          ______________________________________                                    

These tables also show the advantages of blends of the instant inventionas evidenced by the lower torque values required to reach fusion peak asopposed to the torque value required when a liquid stabilizer such asepoxidized soybean oil is used. The melting point of theethylene/glycidyl methacrylate copolymer (102° C) is also high enough sothat it will not lower the glass transition temperature (softeningpoint) of the finished product when blended with the PVC composition ofthe instant invention.

It is to be understood that this invention is not restricted to theforegoing examples which serve only to illustrate the present invention.Numerous variations may be devised without departing from the scope ofthis invention.

What is claimed is:
 1. A method for preparing a polyvinyl chloridecomposition which comprises blending with polyvinyl chloride resin about1 to about 50 parts based on 100 parts of resin of a copolymer ofpolypropylene having grafted thereon a saturated epoxy monomer selectedfrom the group consisting of glycidyl methacrylate, glycidyl acrylate,allyl glycidyl ether, vinyl glycidyl phthalate and allyl glycidylphthalate, wherein said composition has improved thermal stability and aglass transition temperature equal to or greater than the glasstransition temperature of the polyvinyl chloride resin.